1. Field of the Invention
The present invention relates to a charge coupled device. More particularly, this invention relates to a charge coupled device enabling an image recording/reproducing medium such as a camcorder to realize a reverse image.
2. Discussion of Related Art
A reverse image is the image of which left, right, upper and lower directions are changed by regulating the angle of the LCD for use of a view finder attached to a camcorder, so that a person who is taken a picture of can directly view the screen from the position where he is.
With reference to the attached drawings, a conventional charge coupled device will be described below.
As illustrated in FIG. 1, the conventional charge coupled device includes: a plurality of matrix-type photo diode areas 1 formed on an image sensing area; a plurality of VCCDs 2 formed vertically to one side of each photo diode area 1, and transmitting charges formed in the photo diode areas; an optical black area 3 formed around the image sensing area; an HCCD 4 formed on one side of each VCCD 2 and transmitting the signal charges transmitted through the VCCDs 2 in a horizontal direction; and a sensing amplifier 5 formed on one side of the HCCD 4, sensing the transmitted charges and outputting them to outside.
A unit cell, a part of FIG. 1, of the above-mentioned charge coupled device is structured as follows.
As illustrated in FIGS. 2A to 2C, the unit cell includes: a first p type well 7 formed on an n type semiconductor substrate 6; a photo diode area 8 formed of a PD-N layer and a PD-P layer on the first p-type well 7; a high concentration p type impurity diffusion area 11 formed on the photo diode area 8 excluding one side of the area 8 to which the signal charges are transferred, and therefore used as a channel stop layer; a second p type well 9 formed on the portion of the first p type well 7 where the photo diode area and high concentration p type impurity diffusion area 11 are not formed; an N type impurity diffusion area 10 formed in the second p type well 9 and used for the VCCD area; first and second polysilicon gate electrodes 12 (the first polysilicon gate electrode is not shown in FIG. 2B) insulated by first insulating layer 13 which is formed on the overall surface of the substrate, and formed on the n type impurity diffusion area 10; a light blocking metal layer 14 formed on a portion other than the photo diode area 8; a second insulating layer 15 formed on the overall surface of the substrate; a color filter layer 16 formed on the second insulating layer 15 on the photo diode area 8, and transmitting a radiation of a specific wave; a third insulating layer 17 formed on the overall surface of the substrate including the color filter layer 16; and a micro lens 18 formed on the third insulating layer 17 on the color filter layer 16 and thus focusing light.
Here, the first insulating layer 13 is made up with a gate insulating layer which is formed on the overall substrate before the first polysilicon gate electrode is formed, and an insulating layer formed on the second polysilicon gate electrode.
A potential profile of the thus-structured charge coupled device's photo diode area is shown in FIG. 2C. The photo diode area 8 and its lower side are made up with the PD-P, PD-N, the first p type well, and the n type semiconductor substrate.
The PD-N area is fully depleted by the PD-P and the first p type well. Here, the highest potential of the PD-N area is the photo diode pinch-off voltage.
In FIG. 2C, Vsdl indicates the lowest voltage of the first p type well. Vsht is the vertical potential profile. Vofd is DC voltage applied to the n type semiconductor substrate.
A charge transmitting operation of the conventional charge coupled device will be described below.
FIG. 3 is a sectional view of the VCCD area. The first and second polysilicon gate electrodes are alternatively formed on the VCCD area. The signal charges, placed in the VCCD area under the first and second polysilicon gate electrodes to which vertical clock signals V.phi.1, V.phi.2 are applied at the time point T=1, are shifted under the first and second polysilicon gate electrodes to which the next vertical clock signals V.phi.1, V.phi.2 are applied at the time point T=9, by using the clock signal applied to the VCCD. A rising time (RT) of the clock signal applied to the VCCD area may be fast, but the falling time (FT) should not be too fast because the signal charges are not shifted in the foregoing direction, but remain or shift to the reverse direction, thereby lowering the charge transmitting efficiency.
The image recording/reproducing medium such as the camcorder using the conventional solid state device multi-functions to thereby provide the user specific services. The camcorder should provide the above-mentioned reverse image which enables the object, a people to watch the picture screen from the position where he is filmed.
However, the conventional charge coupled device displays the image in a reverse way because the transmission of the signal charge is made in one direction.